In hospitals hypodermic syringes are frequently pre-filled with a particular dosage at the hospital pharmacy and then transferred to the hospital floor for administration to the patient. Frequently a diluent liquid, such as normal saline or sterile water, is added to a small amount of medication in a syringe to change the medication's concentration. These diluents, and sometimes the medications themselves, are supplied in bulk containers to the pharmacy. The pharmacist fills many hypodermic syringes from a single bulk container.
In the past, there have been complicated systems for connecting and disconnecting a series of syringes with a bulk container of liquid. These sometimes included rotatable stopcocks to start and stop the flow of liquid. This stopcock twisting procedure became very time consuming and tedious when several hundred syringes had to be filled during a day.
Another approach was to use a sharpened hypodermic needle on each syringe to puncture a rubber diaphragm to gain access to the sterile contents of the large reservoir container. A high number of repeated punctures through a single rubber diaphragm causes a problem in mechanical deterioration of the rubber. Small bits of rubber could be sucked into the syringe through its sharp piercing needle during filling.